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<h3>ADODB Session Management Manual</h3>
<p>
V4.22 15 Apr 2004 (c) 2000-2004 John Lim (jlim#natsoft.com.my)
<p> <font size=1>This software is dual licensed using BSD-Style and LGPL. This 
  means you can use it in compiled proprietary and commercial products. </font> 
<p>Useful ADOdb links:  <a href=http://php.weblogs.com/adodb>Download</a> &nbsp; <a href=http://php.weblogs.com/adodb_manual>Other Docs</a>

<h3>Introduction</h3>
<p> 
We store state information specific to a user or web client in session variables. These session variables 
 persist throughout a session, as the user moves from page to page. 
<p>
To use session variables, call session_start() at the beginning of your web page, 
before your HTTP headers are sent. Then for every variable you want to keep alive 
for the duration of the session, call session_register($variable_name). By default, 
the session handler will keep track of the session by using a cookie. You can save objects
 or arrays in session variables also.
<p>The default method of storing sessions is to store it in a file. However if 
  you have special needs such as you:
<ul>
  <li>Have multiple web servers that need to share session info</li>
  <li>Need to do special processing of each session</li>
  <li>Require notification when a session expires</li>
</ul>
<p>Then the ADOdb session handler provides you with the above additional capabilities 
  by storing the session information as records in a database table that can be 
  shared across multiple servers. 
<p><b>Important Upgrade Notice:</b> Since ADOdb 4.05, the session files have been moved to its own folder, adodb/session. This is a rewrite
of the session code by Ross Smith. The old session code is in adodb/session/old. 
<h4>ADOdb Session Handler Features</h4>
<ul>
<li>Ability to define a notification function that is called when a session expires. Typically
used to detect session logout and release global resources.
<li>Optimization of database writes. We crc32 the session data and only perform an update
to the session data if there is a data change.
<li>Support for large amounts of session data with CLOBs (see adodb-session-clob.php). Useful
for Oracle.
<li>Support for encrypted session data, see adodb-cryptsession.inc.php. Enabling encryption 
is simply a matter of including adodb-cryptsession.inc.php instead of adodb-session.inc.php.
</ul>
<h3>Setup</h3>
<p>There are 3 session management files that you can use:
<pre>
adodb-session.php        : The default
adodb-session-clob.php   : Use this if you are storing DATA in clobs
adodb-cryptsession.php   : Use this if you want to store encrypted session data in the database

<strong>Examples</strong>
 <font color=#004040>
    include('adodb/adodb.inc.php');
    
<b>    $ADODB_SESSION_DRIVER='mysql';
    $ADODB_SESSION_CONNECT='localhost';
    $ADODB_SESSION_USER ='scott';
    $ADODB_SESSION_PWD ='tiger';
    $ADODB_SESSION_DB ='sessiondb';</b>
    
    <b>include('adodb/session/adodb-session.php');</b>
    session_start();
    
    #
    # Test session vars, the following should increment on refresh
    #
    $_SESSION['AVAR'] += 1;
    print "&lt;p>\$_SESSION['AVAR']={$_SESSION['AVAR']}&lt;/p>";
</font>
To force non-persistent connections, call adodb_session_open first before session_start():
 <font color=#004040>
    include('adodb/adodb.inc.php');
    
<b>    $ADODB_SESSION_DRIVER='mysql';
    $ADODB_SESSION_CONNECT='localhost';
    $ADODB_SESSION_USER ='scott';
    $ADODB_SESSION_PWD ='tiger';
    $ADODB_SESSION_DB ='sessiondb';</b>
    
    <b>include('adodb/session/adodb-session.php');
    adodb_sess_open(false,false,false);</b>
    session_start();
 </font color=#004040>
To use a encrypted sessions, simply replace the file:
 <font color=#004040>
    include('adodb/adodb.inc.php');
    
<b>    $ADODB_SESSION_DRIVER='mysql';
    $ADODB_SESSION_CONNECT='localhost';
    $ADODB_SESSION_USER ='scott';
    $ADODB_SESSION_PWD ='tiger';
    $ADODB_SESSION_DB ='sessiondb';
    
    include('adodb/session/adodb-cryptsession.php');</b>
    session_start();
    </font>
And the same technique for adodb-session-clob.php:
 <font color=#004040>
    include('adodb/adodb.inc.php');
    
<b>    $ADODB_SESSION_DRIVER='mysql';
    $ADODB_SESSION_CONNECT='localhost';
    $ADODB_SESSION_USER ='scott';
    $ADODB_SESSION_PWD ='tiger';
    $ADODB_SESSION_DB ='sessiondb';
    
    include('adodb/session/adodb-session-clob.php');</b>
    session_start();
    </font>
 <h4>Installation</h4>
 1. Create this table in your database (syntax might vary depending on your db):
 <a name=sessiontab></a> <font color=#004040>
  create table sessions (
       SESSKEY char(32) not null,
       EXPIRY int(11) unsigned not null,
       EXPIREREF varchar(64),
       DATA text not null,
      primary key (sesskey)
  );</font>
  
  For the adodb-session-clob.php version, create this:
   <font color=#004040>
    create table sessions (
       SESSKEY char(32) not null,
       EXPIRY int(11) unsigned not null,
       EXPIREREF varchar(64),
       DATA CLOB,
      primary key (sesskey)
  );</font>

  2. Then define the following parameters. You can either modify
     this file, or define them before this file is included:
      <font color=#004040>
    $ADODB_SESSION_DRIVER='database driver, eg. mysql or ibase';
    $ADODB_SESSION_CONNECT='server to connect to';
    $ADODB_SESSION_USER ='user';
    $ADODB_SESSION_PWD ='password';
    $ADODB_SESSION_DB ='database';
    $ADODB_SESSION_TBL = 'sessions'; # setting this is optional
	</font>
    When the session is created, $<b>ADODB_SESS_CONN</b> holds the connection object.
    
  3. Recommended is PHP 4.0.6 or later. There are documented session bugs 
  in earlier versions of PHP.
</pre>

    <h3>Notifications</h3>
<p>If you want to receive notification when a session expires, then
     tag the session record with a <a href="#sessiontab">EXPIREREF</a> tag (see the 
    definition of the sessions table above).  Before any session record is deleted,
	ADOdb will call a notification function, passing in the EXPIREREF.
<p>
When a session is first created, we check a global variable $ADODB_SESSION_EXPIRE_NOTIFY.
    This is an array with 2 elements, the first being the name of the session variable
    you would like to store in the EXPIREREF field, and the 2nd is the 
    notification function's name.
	<p>
	 Suppose we want to be notified when a user's session 
    has expired, based on the userid. The user id in the global session variable $USERID.
	The function name is 'NotifyFn'. So we define:
    <pre> <font color=#004040>
        $ADODB_SESSION_EXPIRE_NOTIFY = array('USERID','NotifyFn');
    </font></pre>
    And when the NotifyFn is called (when the session expires), we pass the $USERID 
    as the first parameter, eg. NotifyFn($userid, $sesskey). The session key (which is 
	the primary key of the record in the sessions table) is the 2nd parameter.
  <p>
    Here is an example of a Notification function that deletes some records in the database
	and temporary files:
    <pre><font color=#004040>
        function NotifyFn($expireref, $sesskey)
        {
        global $ADODB_SESS_CONN; # the session connection object

          $user = $ADODB_SESS_CONN->qstr($expireref);
          $ADODB_SESS_CONN->Execute("delete from shopping_cart where user=$user");
          system("rm /work/tmpfiles/$expireref/*");
        }</font>
    </pre>
	<p>
 	NOTE 1: If you have register_globals disabled in php.ini, then you will have to
	manually set the EXPIREREF. E.g.
	  <pre> <font color=#004040>
	    $GLOBALS['USERID'] =& $_SESSION['USERID'];
        $ADODB_SESSION_EXPIRE_NOTIFY = array('USERID','NotifyFn');
    </font></pre>
    <p>
    NOTE 2: If you want to change the EXPIREREF after the session record has been
    created, you will need to modify any session variable to force a database
    record update.

<h4>Neat Notification Tricks</h4>

<p><i>ExpireRef</i> normally holds the user id of the current session.
<p>
1. You can then write a session monitor, scanning expireref to see
who is currently logged on.
<p>
2. If you delete the sessions record for a specific user, eg.
<pre>
delete from sessions where expireref = '$USER'
</pre>
then the user is logged out. Useful for ejecting someone from a
site.
<p>
3. You can scan the sessions table to ensure no user
can be logged in twice. Useful for security reasons.
<p>

<h3>Compression/Encryption Schemes</h3>
Since ADOdb 4.05, thanks to Ross Smith,  multiple encryption and compression schemes are supported.
  Currently, supported:
<pre>
  MD5Crypt (crypt.inc.php)
  MCrypt
  Secure (Horde's emulation of MCrypt, if MCrypt module is not available.)
  GZip
  BZip2
</pre>
These are stackable. E.g. 
<pre>
ADODB_Session::filter(new ADODB_Compress_Bzip2());
ADODB_Session::filter(new ADODB_Encrypt_MD5());
</pre>
will compress and then encrypt the record in the database.
<p>
Also see the <a href=docs-adodb.htm>core ADOdb documentation</a>.
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